CONDITION REFERENCE
Mitochondrial complex I deficiency
Information from MedlinePlus Genetics about this condition and how it can be inherited.
About this condition
Mitochondrial complex I deficiency is a shortage (deficiency) of a protein complex called complex I or a loss of its function. Complex I is found in cell structures called mitochondria, which convert the energy from food into a form that cells can use. Complex I is the first of five mitochondrial complexes that carry out a multi-step process called oxidative phosphorylation, through which cells derive much of their energy.
Mitochondrial complex I deficiency can cause a wide variety of signs and symptoms affecting many organs and systems of the body, particularly the nervous system, the heart, and the muscles used for movement (skeletal muscles). These signs and symptoms can appear at any time from birth to adulthood.
People with mitochondrial complex I deficiency typically have neurological problems, such as abnormal brain function (encephalopathy), recurrent seizures (epilepsy), intellectual disability, difficulty coordinating movements (ataxia), or involuntary movements (dystonia). Affected individuals may have low muscle tone (hypotonia), muscle pain (myalgia), and extreme fatigue in response to physical activity (exercise intolerance). They tend to develop elevated levels of lactic acid in the blood (lactic acidosis), which can cause nausea, vomiting, weakness, and rapid breathing. In severe cases, lactic acidosis can be life-threatening.
People with mitochondrial complex I deficiency sometimes have heart, liver, or kidney problems. Vision problems due to abnormal eye movement or breakdown (degeneration) of the nerves that carry signals from the eyes to the brain (optic nerves) can also occur.
Some people with mitochondrial complex I deficiency have groups of signs and symptoms that are classified as a specific syndrome. For example, a condition called Leigh syndrome is most commonly caused by mitochondrial complex I deficiency. Leigh syndrome is characterized by progressive loss of mental and movement abilities (developmental or psychomotor regression) and typically results in death within 2 to 3 years from the onset of symptoms. Another condition that can be caused by mitochondrial complex I deficiency, Leber hereditary optic neuropathy, is associated mainly with vision problems due to optic nerve degeneration. These syndromes can also have other causes.
Inheritance
- X-linked
- Mitochondrial
- Autosomal recessive
A condition can have several forms with different inheritance patterns. Each pattern may apply to a different gene or form of the condition.
Related genes
MedlinePlus lists these genes for this condition. Open a gene page to read any available ClinGen reviews and ClinVar records.
YOUR DNA FILE
What can your DNA file tell you?
Your DNA file only includes the positions your test checked and reported. Consumer DNA kits usually test selected positions. Sequencing files can also leave out positions that were not reported or where the test could not give a result.
A variant missing from your file does not mean you tested negative for it. A ClinVar classification applies to a particular variant and the condition or finding it was reported for. It does not apply to everyone with that gene. An uncertain finding cannot establish a diagnosis.
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Sources and dates
The source information on this page last changed on 2026-09-18.
MedlinePlus Source details
Source release: Fri, 18 Sep 2026 05:17:13 GMT
Source publication: 2020-08-18
Source review: 2017-10
SHA-256: fdc8bd614310c12718379cef6569962e5d0e791cecabcc355b53a72816ac263a
About the library sources · Latest validated release · Record 46138f36c928